<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <meta http-equiv="X-UA-Compatible" content="ie=edge" />
    <title>Document</title>
    <style>
      div {
        display: flex;
        width: 80%;
        height: 300px;
        background-color: red;
        /* 让三个子盒子沿着侧轴底侧对齐 */
        /* align-items: flex-end; */
        /* 我们想只让3号盒子下来底侧 */
      }

      div span {
        width: 150px;
        height: 100px;
        background-color: purple;
        margin-right: 5px;
      }

      div span:nth-child(2) {
        /* 默认是0   -1比0小所以在前面 */
        order: -1;
      }

      div span:nth-child(3) {
        align-self: flex-end;
      }
    </style>
  </head>

  <body>
    <div>
      <span>1</span>
      <span>2</span>
      <span>3</span>
    </div>
  </body>
</html>
